SARS-CoV-2 seroprevalence in Spain

We read with great interest the Article by Marina Pollán and colleagues.¹ It is remarkable that in the Spanish popu­la­tion, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seroprevalence as of May, 2020, appeared to be the same in men (immunoassay positive 4·6%, 95% CI 4·2–5·0) and women (4·6%, 4·2–5·0). Of note, neither Pollán and colleagues nor Eckerle and Meyer’s linked Comment² mention the sex distri­bution throughout different age strata. This is a missed opportunity because Spain, among other countries, showed marked age-specific sex differences among confirmed SARS-CoV-2 cases during the first months of the pandemic.³

To depict this difference, we used data provided by governmental health authorities from countries in Europe, as well as the USA and Canada (appendix). In all 12 countries with data available on sex distribution across different ages, the proportion of men with confirmed SARS-CoV-2 was lower than for women in the age group older than 80 years, and was similar to the proportion of older men in the general population. Additionally, some countries also showed sex differences in younger age groups. For example in Spain, as of May 5, 2020, the proportion of men aged 20–39 years with confirmed SARS-CoV-2 was only 36% (women accounted for 64%),³ which was markedly lower than the proportion of men (50%) aged 20–39 years reported in the general population.⁴

Nationwide seroepidemiological studies such as ENE-COVID¹ should provide details on age-stratified sex distribution to clarify whether sex differences are due to the testing policies or acceptability, or due to expo­sure differences (ie, more women in high risk groups such as health-care workers). In countries with large sex differences, such as Belgium, the UK, or Spain, this information might help to elucidate whether SARS-CoV-2 diagnoses have been disproportiona­tely overlooked in specific populations (eg, in young men).